The present invention relates to a sealing element for producing smooth stamping fields during the sealing of two plastic sheets.
During the production of blister packs, especially in the pharmaceutical industry, a forming sheet with molded-in pockets, into which the products are placed, is produced first. Then, in a sealing station of a thermoforming machine, a cover sheet is sealed to the forming sheet in the areas outside the pockets. The sealing station can be operated continuously with sealing rolls rolling against each other or discontinuously with opposing sealing plates. After the two plastic sheets have been sealed together, it is often necessary to stamp lot numbers or other information in a targeted and indelible manner on the blister band which has been produced. So that the mechanically stamped information can be read more easily, the area required to accept it, namely, the coding or stamping field, is not sealed with two conventional sealing tools, because the ripples on the surface of the sealing tools would produce waviness in the cover sheet. Instead, one of the two sealing tools contains, in the area of the desired stamping field, a sealing element, which is introduced into a recess in the sealing tool and supported there by a spring mechanism. Because the spring is subjected to constant loading, however, it undergoes heavy wear, and the spring characteristic can also change as a result.
To reduce the susceptibility of the sealing element, a spring mechanism integrated into the sealing element has been proposed in DE 10 2006 010 023 B3. For this purpose, two slots are provided in the sealing element. The slots are offset from each other vertically and extend into the opposite sides of the base body of the sealing element. Between them a thin bending beam is formed, which can be deformed elastically under mechanical pressure. Even with these types of sealing elements, however, it is impossible to prevent wear from occurring as a result of material fatigue, and in particular these types of sealing elements can be plastically deformed and thus destroyed when they are subjected to excessive pressure as a result of operating error.